Electrical device



April 30, 1946. E. c. WAHLBERG ELECTRICAL DEVICE Filed Jan. 15, '1945 3Sheets-Sheet 1 EN TOR.

aim/1%;

By 7114mm E. c. WAHLBERG 2,399,273

ELECTRICAL DEVICE Filed Jan. 15, 1945 3 Sheets-Sheet 2 April 30, 1946.=

IN V EN TOR.

April 30, 1946. E. c. WAHLBERG ELECTRICAL DEVICE Filed Jan. 15, 1943 3Sheets-Sheet I5 INVENTOR. a (Z z/bwm Patented Apr. 30, 1946 UNITEDSTATES PATENT OFFICE ELECTRICAL DEVICE Eric C. Wahlberg, Stamford,Conn., asslgnor to Electrolux Corporation, New York, N. Y., acorporation of Delaware 12 Claims.

This application relates to a system of synchronized rotating electricmachines, more particularly a system of synchronized electric motors ofthe direct current type. This invention constitutes acontinuation-in-part of my prior application Serial No, 428,018 filedJanuary 24, 1942, entitled Electrical devices.

The principal object of this invention is to impr ve the operation ofthe apparatus set forth in the aforesaid application.

It is a further object of this invention to provide such a system whichwill be suitable for protracted operation on a duty cycle consisting ofstarting, running, and stoppin that has a much shorter period than thatpermissible with the apparatus disclosed in the previous application.

Another object of the invention is to reduce the number of wiresinterconnecting the machines of the system, while still maintainingtheir synchronous operation.

Still another object of the invention is to reduce the length of timeconsumed by the stopping portion of the duty cycle of the machines.

Other objects and advantages of the invention will become apparent asthe description of the operation thereof proceeds.

Referring to the drawings forming a. part of the specification, there isshown in Fig. 1 a schematic wiring diagram showing the improved system.Figs. 2 through 4 show modified forms thereof.

Referring to Fig. 1, reference characters l and 2 designate the armatureand field circuits of two electric motors constructed according to myinvention. Each motor has a main armature winding 3, an auxiliaryarmature winding 4, and a field winding 5. The armature windings 3 arerepresented only schematically and may be of any de sired type. For thepurposes of illustration, it will be assumed that the windings 3 aredistributed windings of the lap winding type common to ordinary directcurrent electric motors. The auxiliary winding 4 may also be of ansuitable type, either distributed or concentrated, but for illustration,it will be assumed that they are'in the form of spiral helixes with theconductors occupying slots distributed over the entire armature. Theconductors of the auxiliary winding may, if desired, occupy the sameslots as the conductors of the main winding. The field windings 5 arealso shown schematically. The machines could have any desired number ofpairs of poles but for the purposes of illustration, it is assumed thatthe windings 5 represent the field windings of two-pole machines.

Each 01' the machines I and 2 is provided with a suitable commutator(not shown), to which are connected suitable taps from the main windings3. Each machine is provided with brushes 6 and I which in the actualmachine would rest on the commutators of the machines. In the schematicdrawings the brushes are shown resting directly on the windings 3. Thebrushes 6 and l' of each machine are connected to conductors l5 and I6and these conductors are connected in parallel with one another byconductors l1 and I8. Conductors I1 and it are connected to a D. C.supply ll through a switch IS. A switch 23 is provided for shortcircuiting the conductors l1 and I8.

Taps l and 8 are taken from the main winding 3 f each machine. One endof each auxiliary winding 4 is connected to a tap.8 and the other end ofeach auxiliary winding is connected to a conductor 9. The tap l andconductor 9 of each machine are connected to slip rings in the manner ofa rotary converter. The slip rings of each machine are connected inparallel with those of the other machine by conductors II and I2. Theconductors II and I2 are also connected through a switch l3 to thesource of direct current potential ll.

The fields 5 of the machines are connected in parallel and are alsoconnected to the source of direct current H.

Inone form of the invention, as described later, reversing switches 20and 2| may be provided in the connection of the field windings to the D.C. supply and in the interconnection between the slip rings of themachines respectively. There may also be provided a main switch 22 forcontrolling the application of power from the D. C. supply H to theentire system.

The operation of the system set forth above will now be described.Assume that the reversing switches 20 and 2i are closed to the polesnearest to the illustrated positions of the switches. As-

sume also that the remaining switches l3, I9, 22

and 23 are open. The switch 22 is first closed to energize the system.The switch I3 should be closed next. This will supply direct current tothe armature windings of each of the machines through the taps l andconductors 9. The current will fiow in parallel paths through the twohalves of the main windings between the taps I and 8 and thence throughthe auxiliary windings 4. It is assumed that the main armature windingwill produce a flux, the axis of which bisects the angle between thetaps l. and 8, and that the auxiliary windings l produce a flux havingan axis coinciding with the axis of the flux produced by the mainwindings. Thus. there will be produced in the armature of each machine apair of fixed poles. These poles will line up with the main field polesoi each machine which are energized by the windings l. The armature ofeach machine will thus be brought into the same'space relationship withits field poles as that of each of the other machines.

After sufficient time has elapsed to permit the armatures of themachines to be positioned before starting, the switch. 13 is opened andthe switch I9 is closed. Closure of switch it applies direct currentthrough the commutator (not shown) to the main armature windings only ofeach of the machines and they will accelerate as ordinary direct currentmotors. During this period there I will be alternating current voltagesgenerated between the taps 'l and conductors 9 of each machine. Shouldone of the machines tend to accelerate faster than the other, itsalternating voltages would get out of phase with the alternatingvoltages of the other machine and also would be of greater magnitude andfrequency. This would permit alternating currents to flow between thefast machine and the slow machine and the action of these currents wouldbe to increase the speed of the slow machine and slow down the fastmachine until they are again synchronized. When the machines reachnormal running speed they will continue to operate in synchronism andany tendency for the machines to get out of step will be opposed by theflow of alternating currents between the machines as described for theacceleration period. The importance of positioning the armatures of themotors before starting lies in the fact that the motors will rarely gointo synchronization when started under load if their armatures are notfirst brought into alignment. Even when started without load the motorswill frequently hunt without synchronizing it started from out of phasepositions.

When it is desired to stop the machines. the switch i9 is opened andthen the switch I! is closed. The removal of direct current potentialfrom the commutator brushes of the machines causes them to cease tooperate as motors and they begin to slow down. As the machines slow downthere continue to be alternating voltages generated between the taps Iand conductors 8 of each machine and should one of the machines tend toslow down faster than the other, there would be a flow of alternatingcurrents between the machines through the conductors H and i2 tending tomaintain the machines in synchro nism just as during the starting andrunning period. The application of direct current to the slip rings ofthe machines again produces fixed poles in their armatures as describedpreviously. The flux produced by the poles in the armature cuts thecoils of the field windings ii as the armatures rotate relativelythereto. This generates alternating voltages in the field coils andshould the machines tend to get out oi synchronism, there will be a flowof synchronizing alternating currents between the field windings I whichwill aid the alternating currents flowing in conductors l i and i2 inmaintaining the machines in step. Because of this additionalsynchronizing connection between the machines, they can be maintained instep down to at least the last half revolution of the stopping period.

The alternating voltages generated in the field coils B may also causecurrents to flow through the low resistance paths provided by thearmatures of the several machines to which they arr. connected by themain power lines 24 and 2! and also through the armatures or otherwindings oi the apparatus forming the direct current supply l4. Thisflow of alternating current from the field coils through the armaturesof the machines will consume energy which must be supplied by thekinetic energy of rotation of the armatures and hence produces a dynamicbraking of the machines.

There will be a further dynamic braking action due to the generation ofalternating voltages between the taps 1 and conductors 9 of the armaturewindings which will cause a flow oi alternating currents through thefield windings 5 of the machines to which they are connected byconductors 2d and 25 and also through the windings of the apparatusconstituting the source of direct current M.

To supplement the dynamic braking action due to the how of alternatingcurrents as described above. the switch 23 may be closed during thestopping period. Preferably the switch 23 is closed at the same timeswitch 13 is closed. Closure of switch 23 will provide a short circuitpath for the flow of direct current between the brushes 6 and l oi eachof the machines. The provision of this additional path for the flow ofdynamic braking currents considerably reduces the deceieration time ofthe machines.

The quick stopping of the machines due to dynamic braking reduces theperiod oi time during which the machines have an opportunity to get outof step. This, in combination with the strong synchronizing action dueto the flow of alternating currents between the field windings andbetween the armature windings of the machines. as previously described,effectively maintains synchronism of the machines at least down to thelast half revolution of the stopping period.

Should the machines tend to get out of step dur ing the last halfrevolution of their operation, they will be brought back intosynchronism by the action of the fixed armature poles tending to line upwith the fixed poles of the main field, just as during the initialalignment of the armatures of the machines prior to the startingthereof.

Since the armatures of the motors are thus brought to rest in exactalignment, it is unnecessary'to position them again before startingunless they have been disturbed in the interim. Hence, in someapplications it is only necessary to apply direct current to the sliprings during the stopping period. On the other hand there areapplications in which it is immaterial whether or not the motors arebrought to rest in synchronization, and in such cases direct currentneed be applied to the slip rings to position the armatures only beforethe motors are started and not during the stopping period.

It is to be noted from the above described operation of the system ofsynchronized motors according to this invention, that only two wires areused to interconnect the alternating current sides of the motors. Thesystem disclosed in the prior application Serial No. 428,018, referredto previously, used three wires interconnecting the alternating currentsides of the machines. The third wire has since been found unnecessaryand its elimination makes the system much more desirable, both from themanufacturing standpoint and that of the user.

The purpose or the auxiliary armature windings 4 will now be considered.By the use of these auxiliary windings. the magnitude of the currentasoaavs flowing in the main field winding when the switch II is closedis reduced because oi the resistance of the auxiliary winding ll.However, the auxiliary winding ll being wound on the same core as themain armature winding 3 produces additional ampere turns which balancethe reduction in ampere turns of the combined armature windings ing andalso reduces the size oi relays necessary to carry on the switchingoperations.

Although the intended purpose of the auxiliary windings is as justdescribed, it is to be noted that whenever the armatures are rotatingthere are alternating potentials generated in them. Since the auxiliarywinding is wound so that its magnetic flux is in the same direction asthat produced by the main winding when the motors are connected todirect current for positioning, it is obvious that the alternatingvoltages generated in them when moving are likewise additive. Hence. itis possible to have a much higher synchronizing voltage by using theauxiliary windings than could be obtained by tapping into the mainwindings alone. By using high voltages in the synchronizing connectionit is apparent that larger synchronizing current will flow between themachines for any given difference in phase between their armatures.Thus, by using the auxiliar winding closer synchronous operation isobtained for a given difference in loads on the motors.

The purpose of the reversing switches 20 and 2| will now be disclosed.In the manufacture of electric machinery it is desirable that all unitsbe manufactured in the same way if possible, regardless of the use towhich they are to be put. This means that the same connections will bemade between the armature and the slip rings and between the armatureand brushes and generally between the internal windings oi the machinesand the external connection leads. Likewise, it is desirable that themounting brackets for all of the motors be constituted in a like manner.There are occasions in the use of synchronous machines, such as thosedescribed, in which the apparatus to which they are connected must bedriven in opposite directions even though the apparatus should otherwisebe driven synchronously. The switches 20 and 2| shown in the schematicdiagram of Fig. 1 are merely to indicate that by reversing both thefield connections and the connections to one of the motors between thealternating current sides of the machines they may be maintained insynchronism although driven in opposite directions. The same resultcould also be obtained by reversing the connection to one of the mainarmature windings from the D. C. supply instead of reversing the fieldconnections. The switches need not actually be used in practice, havingbeen illustrated merely to indicate how the connections should bechanged.

Reference should now be made to Figs. 2, 3 and 4 of the drawings. Inthese figures there are shown modified connections between the armaturewindings of the machines I and 2. Since the rest of the connections arethe same as shown in Fig. 1, they have been omitted. To form a completecircuit, the portion of the circuit shown in any of Figs. 2, 3 and 4 maybe substituted for that portion of the circuit of Fig. 1 enclosed in thebox formed by dashed lines.

In the circuit shown in Fig. 2, the auxiliary winding 4 has been placedin series with the tap I from the armature winding of machine 2 insteador in series with tap 8. With this arrangement, balanced currents flowin the lines II and I2 interconnecting the alternating current sides ofthe machines. The operation is otherwise the same as that of the circuitshown in Fig. 1.

In Fig. 3, the auxiliary windings l have been connected in parallel withone another between the conductor II from the main power source and aconductor 12a. The portions of the main armature windings 3 includedbetween the taps I and l of the two motors are connected in parallelwith each other between the conductors II and Ila. The synchronizingcurrents developed in said portions of the main armature windings and inthe auxiliary windings. respectively, thus flow through parallel pathsand hence there is less resistance to the flow of these currents betweenthe motors. The operation of the circuit is otherwise the same as theoperation described in connection with Fig. 1. g I,

In Fig. 4, the auxiliary winding 4 of machine I is connected in serieswith the main power line going to conductor l2, the same as in Fig. 3.The auxiliary winding 4 of machine 2, however, is connected in serieswith the main power line leading to conductor I l With this arrangement,a result similar to that obtained with the Fig. 3 circuit is obtainedbut there is a reduction in the magnitude of the current flowing to'thearmatures of the machines during the stopping period. Such anarrangement may be desirable to balance the available voltage supply tothe resistance of the particular main armature windings selected.

In the description of the invention just set forth, manualoperation ofthe various switches I3, l8 and 23 was described. It should beunderstood, however, that these switches or their equivalents may beoperated automatically in the manner set forth in the previousapplication Serial No. 428,018. Furthermore, while the field windings ofthe machines have been shown connected in parallel and connected to thesame source of supply as the armatures of the machines, they may, ifdesired, be connected in series and/or connected to a separate source ofpower. Such connections have not been illustrated in this application asa full description thereof appears in the prior application Serial No.428,018, referred to above.

It should also be pointed out that two of the principal features of theinvention set forth in this application, namely, two wiresynchronization and the use of the auxiliary winding, are equally asapplicable to alternating current machines as to direct currentmachines, and as a matter of fact, the motors illustrated are of theuniversal type, and hence will operate satisfactorily on eitheralternating or direct current. To obtain full benefits of the two wiresystem in alternating current machinery, single phase machines, such asthose shown, should be used. With such an arrangement, there need be buttwo wires interconnecting the machines as the same wires are used duringthe starting and stopping periods as during the running period. Duringpositioning, if alternating current is employed, the polarities of thefield poles are reversed in accordance with the frequency of thecurrent, but at the same time the polarities oi the relatively fixedpoles established in the armatures are likewise reversed in the samemanner and consequently the armatures are positioned relative to theirfields when using alternating current in the same manner as describedfor direct curren operation.

From the description of this invention as set forth above, it isbelieved that the manner of obtaining all of the objects set forth inthe first part of the specification will be apparent. While a preferredembodiment of the invention has been described, it is understood thatthis was for purposes of illustration only and that many changes andmodifications may be made therein. It is intended to cover by theseLetters Patent all forms of the invention falling within the scope ofthe appended claims.

Certain subject matter disclosed but not claimed in the presentapplication is claimed in my copending divisional application Serial No.633,325 filed December 7, 1945.

What I claim is:

l. A plurality of rotary converters, means connecting in parallel thealternating current sides of the converters, means for operating theconverters as motors from their direct current sides, an auxiliarywinding on the armature of each converter, means to apply direct currentto the alternating current sides of the converters and to the auxiliarywindings to produce magnetic poles in the armatures of the convertersfixed with respect to the armatures, and means to short circuit thecommutators of each of the converters.

2. A plurality of electric motors each having a field winding and anarmature winding, two conductors interconnecting fixed taps taken fromthe armature winding of each machine, a commutator for each armaturewinding, means to apply electric current to the commutator of eachmachine, and means to apply electric current to the fixed taps from thearmature of each machine.

3. A plurality of electric motors each having a field winding and anarmature winding, two conductors interconnecting fixed taps taken fromthe armature winding of each machine, a commutator for each armaturewinding, means to apply electric current to the commutator of eachmachine, means to apply electric current to the fixed taps from thearmature of each machine, and means to short circuit the commutator ofeach machine.

4. A plurality of electric motors each having a field winding and a mainarmature winding and an auxiliary armature winding, two conductorsinterconnecting fixed taps taken from the armature winding 01 eachmachine, a commutator for each main armature winding, means to applyelectric current to the armature or each machine, and means to applyelectric current to the fixed taps from the armature of each machine andalso to the auxiliary armature winding of each machine to produce fixedmagnetic poles in the armature of each machine with the main andauxiliar windings aiding one another.

5. A plurality of electric motors each having a field winding and a mainarmature winding and an auxiliary armature winding, two conductorsinterconnecting fixed taps taken from the armature winding of eachmachine, a commutator for each main armature winding, means to applyelectric current to the armature of each machine, means to applyelectric current to the fixed taps from the armature of each machine andalso to assume the auxiliary armature winding 01 each machine to producefixed magnetic poles in the armature of each machine with the main andauxiliary windings aiding one another, and means to short circuit thearmature 0: each machine.

6. A plurality of single phase alternating current motors each having afield winding and a main armature winding and an auxiliary armaturewinding, wires interconnecting the main armature windings of eachmachine, means to apply alternating current to the main armature windingof each machine, and means to apply direct current to both the armaturewindings oi each machine to produce fixed magnetic poles in the armatureof each machine with the main and auxiliary armature windings aidingeach other.

7. A plurality of single phase alternating current motors each having afield winding and a main armature winding and an auxiliary armaturewinding, two wires interconnecting the main armature windings of eachmachine, means to apply alternating current to the main armature windingof each machine, and means to apply direct current to both the armaturewindings of each machine to produce fixed magnetic poles in the armatureof each machine with the main and auxiliary armature windings aidingeach other.

8. A plurality or like constructed electric motors each having anarmature winding and a field winding, means to connect electric power tothe motors to cause them to operate, first taps taken from like pointson the armatures of each motor, second taps taken from like points onthe armatures of each motor, means tying together the first tap 0! atlast one motor and the second tap of at least one other motor and tyingtogether the second tap of the first mentioned motor with the first tapof the second mentioned motor, means connecting the taps of the firstmentioned motors to like taps of all of any remaining motors other thansaid second mentioned motor, the means for connecting the motors toelectric power being such as to cause said first and second mentionedmotors to operate in opposite senses and to cause said all of anyremaining motors to operate in the same sense as said first mentionedmotor, and means to connect direct current to the first and second tapsof said motors.

9. A plurality of electric motors each having a field winding and a mainarmature winding and an auxiliary armature winding, meansinterconnecting fixed taps taken from the main and auxiliary windings ofeach motor with like taps taken from the main and auxiliary windings ofthe other motors, means to apply electric power to the main windings ofeach motor to cause said motors to run, and means to apply directcurrent to both the armature windings of each motor to produce fixedmagnetic poles in the armature of each motor with the main and auxiliarywindings aiding each other.

10. A plurality of electric motors each having a field winding and anarmature winding, means interconnecting fixed taps taken from thearmature winding of each of the motors, a commutator for each armaturewinding, means to apply electric power to the commutator of each motor,means to alternatively apply said electric power to the fixed taps takenfrom the armature of each motor, and means to short circuit thecommutator or each motor at the same time electric power is applied tosaid taps to thereby provide dynamic braking during stopping.

11. A plurality of eiectricmotors each having a stator winding and a.main rotor winding and an auxiliary rotor winding, conductorsinterconnecting the auxiliary windings of each machine,

and means to apply electric current to the stator necting the auxiliarywindings oi each machine, and means to apply electric current to thestator and main rotor windings or each machine to cause the rotors torotate, the rotation of said auxiliary windings in the magnetic fieldspro- I duced by said stator windings inducing alternating cur-rent insaid auxiliary windings for maintaining the rotors in synchronism, andmeans to apply electric current to said auxiliary windings to producerelatively fixed magnetic poles in the rotor of each machine forreacting with the magnetic fields of the stators to align each rotorwith the respective stator. v

ERIC 0. WAHLBERG.

